The Galileo spacecraft made its fifth close fly-by of Io on
August 6, 2001 (orbit I31). Observations by NIMS showed
numerous active volcanic regions and significant changes
since the spacecraft's earlier encounters with Io in 1999
and 2000. The spectral range of NIMS (0.7 to 5.2 microns)
allows the instrument to map the thermal emission from Io's
volcanic regions, and the surface distribution of SO2 and of
other compounds. This paper focuses on thermal mapping (see
Doute' et al, this volume, for spectral analysis). During
I31, NIMS mapped part of Io's anti-Jovian hemisphere, from
north to south pole, at spatial resolution ranging from 22
to 34 km/NIMS pixel. This observation revealed a bright
eruption from about (41N, 136 W), a location not known to be
active previously. This eruption may have included a plume
(A. McEwen, pers.comm.). Numerous previously undetected hot
spots are seen in this observation, mostly concentrated at
low and mid-latitudes. A bright eruption detected during
orbit C30 (May 2001) from a previously undetected hot spot
(49 S, 71W) is still underway. Higher spatial resolution
observations (<20 km/NIMS pixel) allow us to assess
small-scale changes at several active volcanic centers, some
of which were also targeted during the earlier Io fly-bys.
We will present results on the thermal structure of
individual volcanic centers, including Tvashtar,
Amirani/Maui, Prometheus, Pele, Isum, and Gish Bar.
Observations obtained during the fly-bys show that the
structure of these hot spots is more complex than thought
from distant observations and that hot spots are often made
up of more than one volcanic center. Galileo will fly close
to Io's surface again on October 16, 2001 (I32) and several
regions will be targeted that have not yet been observed at
high spatial resolution. We expect to also present some
initial results from this later orbit.